Blood treatment devices with a blood treatment unit, through which blood from a patient flows, are generally known. For example, these include the known haemodialysis, haemofiltration or haemodiafiltration devices. Blood treatment devices can be operated with separate arterial and venous patient connections or with a single patient connection.
When operating a blood treatment device with a single patient connection, blood is removed and returned by means of a single cannula, to which both the arterial and venous blood lines are connected. The blood received from the patient during an arterial phase is stored in a reservoir and is supplied to the patient again from the reservoir in a venous phase.
An extracorporeal blood treatment device is known from WO 2008/148506 A2 in which the blood is conveyed into the blood treatment unit in the arterial phase and is conveyed from the blood treatment unit to a blood collecting vessel, wherein the blood supplied to the patient is interrupted. A predetermined pressure is built up in the blood collecting vessel, which is monitored. Due to the pressure, the blood collected in the blood collecting vessel is displaced from the blood collecting vessel in the venous phase and is supplied to the patient, while the blood supply to the blood treatment unit is interrupted, so that blood does not flow through the blood treatment unit during the venous phase.
When blood does not flow through the dialyser of a dialysis device continuously, there is a risk that the membrane of the dialyser becomes blocked (clotting). Blood treatment devices for single needle operation are known, in which blood flows through the dialyser continuously.
The problem of blockage of the dialyser membrane during the single needle dialysis is addressed in DE 42 17 692 A1, wherein a valve arrangement is proposed for control of fluid flow. In a preliminary step, blood is pumped from the patient by a blood pump via the dialyser into a buffer vessel and, in a following step, is pumped in the same direction of flow from the buffer vessel via the dialyser to the patient again. Between the two steps, the blood circulates by the dialyser in a closed circuit, from which the patient is separated by the valve arrangement, however, so that blood flow through the dialyser is not interrupted.
An extracorporeal blood treatment device for single needle operation with an extracorporeal blood circuit is known from WO 2010/037520 A1, which comprises two occluding pumps, which are positioned in the arterial blood line upstream and downstream of a blood collecting means. Both blood pumps are operated in the arterial and venous phases at different delivery rates. In the arterial phase, a higher delivery rate is set for the blood pump upstream of the blood collecting means than for the blood pump downstream of the collecting means, so that blood is withdrawn from the patient. In the venous phase, however, the delivery rate of the pump upstream of the blood collecting means is lower than the feed rate downstream of the collecting means, so that blood is supplied to the patient. The known device is intended to allow relatively small blood flow rates to be set. A disadvantage is that transmembrane flow over the dialyser membrane is possible.
DE 2 236 433 describes a dialysis device for single needle operation with an extracorporeal blood circuit, in which the blood pump, which is positioned in the arterial blood line upstream of the dialyser, is operated during the arterial and venous phases, so that blood is continuously conveyed through the dialyser. The dialysis device provides an arterial blood reservoir and a pressure chamber. In the arterial phase, the arterial tube clamp in the arterial blood line is open, while the venous tube clamp in the venous blood line is closed, so that blood is pumped from the patient into the pressure chamber. When the pressure in the chamber has reached a predetermined value, in the venous phase the venous tube clamp is opened and the arterial tube clamp is closed, so that blood is supplied from the pressure chamber to the patient. The substantial variations in pressure and pressure peaks occurring upstream of the dialyser have proved to be a disadvantage, since they can lead to an undesired and uncontrolled exchange of blood plasma over the membrane of the dialyser, wherein there is a risk of blocking of the dialyser membrane.